1. Field of the Invention
The present invention relates to the field of polymer modified asphalt compositions and various methods for the preparation of these compositions. More specifically, the present invention relates to a method of making polymer-modified asphalt using an accelerator-gel additive that serves as a carrier for the accelerator in polymer-asphalt formation.
2. Discussion of the Related Art
Polymer-modified asphalt and methods of making polymer-modified asphalt are well known in the art. Polymers, such as thermoplastic elastomer, are commonly bonded with asphalt to improve its strength and performance. It is also know that the stability of the polymer-asphalt compositions can be increased by the addition of sulfur. Sulfur is believed to chemically couple with the polymer and asphalt with sulfide and polysulfide bonds thereby strengthening and accelerating the polymer-asphalt bonding and curing process.
An accelerator such as sulfur may be added to the polymer-asphalt system to enhance the bonding and curing of the polymer and asphalt. Various forms of sulfur accelerators, such as elemental sulfur or sulfur-donating coupling agents including alkyl polysulfide, dithiocarbamates, phosphorous pentasulfide, thiurams, thiazole derivatives, 4,4xe2x80x2-dithiomorpholine are used in polymer asphalt systems. The sulfur may be incorporated with the polymer and asphalt through various methods which typically involve incorporating sulfur in elemental or coupling form into a mixture of polymer and asphalt after the mixture has been agitated for a defined period of time. Alternatively the polymer may be pretreated with sulfur and then the sulfur treated polymer as added to molten asphalt.
Unfortunately, the process of introducing finely divided dry materials, such as sulfur, into reaction vessels or tanks presents an explosion hazard due to the formation and presence of hydrocarbon vapors in combination with elevated processing temperatures. In addition, finely divided dry materials often do not mix thoroughly and efficiently when combined with the liquid material in the system. In an attempt to remedy this problem, the finely divided dry material may be pre-dispersed in oil. However, the tendency for the heavier finely divided material to settle requires constant agitation. More viscous oils and/or asphalt fluxes have been utilized to prevent the settlement of the finely divided material, but the use of these materials requires the application of higher processing temperatures to maintain the oil and or asphalt fluxes at a pumpable viscosity. In addition, this method also requires constant agitation to maintain dispersion of the finely divided material. As a result, the higher temperature need in processing increases the risks of emission of toxic gases, such as hydrogen sulfide, which is highly toxic and flammable. Therefore the processing temperature of highly concentrated sulfur/oil or sulfur/flux systems should not exceed 140xc2x0 F.
In view of the disadvantages discussed above, it is an object of the present invention to provide a stable, composition for delivering accelerator into the liquid polymer-asphalt mixture during the production of polymer modified asphalt.
It is another object of the present invention to provide a stable accelerator-gel suspension that will not separate during storage or during manufacturing processes incorporating its use such as when added to the polymer asphalt system.
It is further an object of the invention to provide a stable accelerator-gel additive that may be premixed and stored at ambient temperature and is of a liquid or gel nature that offers ease of handling and pumpability under normal processing conditions and at temperatures below 140xc2x0 F.
In accordance with the foregoing objectives, the present invention provides a polymer modified asphalt formed through a process incorporating an accelerator-gel additive as an accelerator into the polymer-asphalt liquid material during the production of polymer modified asphalt. The accelerator-gel additive may be used in other asphalt related processes such as xe2x80x9ccatalyticxe2x80x9d air blowing for ease of addition of finely divided solid catalyst such as phosphorous pentoxide or ferric chloride, and addition of finely divided materials to neat asphalt such as calcium carbonate addition to highly acidic asphalts. The accelerator-gel additive may be used in other asphalt related processes such as xe2x80x9ccatalyticxe2x80x9d air blowing for ease of addition of finely divided solid catalyst such as phosphorous pentoxide or ferric chloride, and addition of finely divided materials to neat asphalt such as calcium carbonate addition to highly acidic asphalts. The accelerator-gel additive may also be used as an add mixture in processes other than asphalt or polymer modified asphalt additives. Other processes may include but are not limited to compounding and vulcanization of rubber, and injection, extrusion, and molding of polymeric parts and materials. In addition, the present invention provides a method of making the accelerator-gel additive.
The polymer modified asphalt of the present invention is manufactured through the process of forming an accelerator-gel additive, mixing the accelerator-gel additive with a polymer and asphalt to form a mixture, and curing the mixture at a temperature between approximately 200xc2x0-500xc2x0 F., and preferably between approximately 300xc2x0-400xc2x0 F. The resulting polymer-modified asphalt requires less curing time and provides improved storage stability of the polymer modified asphalt formulation exhibited by resistance to phase separation. In addition to improved curing time and stability, these desirable properties are also achieved faster and more efficiently than in conventional processing systems.
The accelerator-gel additive is a composition comprising; an accelerator, a processing oil, an organophillic clay, and optionally, a polar activator. It is formed through a process comprising; combining the accelerator and the organophillic clay with the processing oil to form a smooth mixture. The polar activator is then added slowly and blended into the mixture to separate platelets in the organophillic clay. This will xe2x80x9cgelxe2x80x9d the oil and thereby suspend the accelerator in a stable form that prevents sedimentation of the accelerator such as finely divided dry sulfur material. Although the accelerator-gel additive is very stable, slight discoloration of the additive may occur over time. This discoloration however, does not effect the performance characteristics of the accelerator-gel additive. The accelerator-gel material is preferably stored in sealed containers to prevent possible oxidation. Slight exudation, if any, of oil may be observed over extended periods of storage. This exudation may be re-incorporated by slight agitation. Increasing the amounts of organophllic clay and polar activator may prevent occurrence of this exudation.
These and other aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description. It should be understood, however, that the following description while indicating the preferred embodiments of the present invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.